In order to further understand the processes involved in transepithelial ion transport, studies must be performed which allow for the differentiation between events taking place at the apical cell membrane and those ocurring at the basolateral membrane. This is especially true since it now seems that Na transport across the apical membrane is not simply diffusional. This strongly indicates that Na regulation by the apical membrane is the major factor in the control of transepithelial Na transport. We propose to study, using electrophysiological methods, the properties of the individual apical and basolateral cell membranes of the Necturus and Amphiuma urinary bladders. Unlike amphibian skins, which have many different cell layers and types, these bladders are anatomically simple while still possessing the electrical properties of a tight epithelium (transmembrane potential difference and resistance on the order of 175mV and 57K omega square cm). Our studies will include both measurements using voltage clamp techniques and ones that will not. The nonvoltage clamp experiments will involve the investigation of intercellular communication via gap junctions and the determination of the space constant of the tissue under various conditions (e.g. different concentrations of Na, Cl, or K in bathing solutions). The voltage clamping of the membranes on one side of the tissue, either the apical or basolateral, will be performed so that we can determine current-voltage relations and carry out current fluctuation (noise) analysis. Independent current-voltage measurements of the apical and basolateral membranes will be conducted with various solutions (e.g., ionic substitution and the addition of blockers of ionic transport such as amiloride, oubain, etc.) bathing the membrane. From these studies we will determine the correlation between membrane potential and conductance and the elements of the bathing solutions. By recording and analyzing current noise under voltage clamp conditions we will be able to make inferences about the events occurring at the apical and basolateral membranes on a molecular level. The types of information derived from noise studies are, single channel conductance and turnover rates, number of sites, and others.